Who knew: I just left my first scientific meeting on consciousness, of an international group funded by a Canadian institution. I was invited to talk about the evolution of the brain and animals that have consciousness.
But the topic of my talk will be for later, because first I want to tell you the coolest thing I learned: brain activity varies depending on the rhythms of the heart, breathing, but also the stomach.
The first two were to be expected. Several studies have shown that rapid eye movements are much more likely during heart systole (a “beat”), when the atrium and then ventricle contract, than between heartbeats. Spontaneous movements in general are also more likely shortly after an inhalation. The reason for this is probably the greater excitability of the cerebral cortex at these times – which naturally raises the following, as yet unanswered, question: why is the cerebral cortex more excitable during systole or inspiration?
What I didn’t expect was to hear that several areas of the cerebral cortex, including regions necessary for introspection and self-awareness, fluctuate in activity with the stomach. The discovery came from a colleague from my PhD, when we were both studying brain physiology and brain waves, and who, to my pleasant surprise, was part of the group meeting in Montreal, to whom I went to speak.
Catherine Tallon-Baudry is now a researcher at the Institute of Medical Education and Research (Inserm) in Paris, France, where she continues to study waves of electrical activity in the brain, which rise and fall in amplitude at each point of the brain and propagate, like sea waves. Accustomed to thinking in sequences of activity, Catherine discovered what others did not see, because they only looked at the parts of the brain that are more or less active at the same time: with each contraction of the stomach, certain regions of the cerebral cortex become sequentially more active, one after the other.
The cortical regions activated by waves from the stomach include parts of the self-referential network, which link our mental activity to our place in space-time and anchor everything in the perception of our own body. These structures form what other researchers call the “default network,” because they have been found to be the parts of the cortex that are most active when you are not in contact with the world, as opposed to the rest of the cortex. In practice, however, it is these structures that make self-referential thinking possible, the beautiful “thinking with your own buttons” in Portuguese that is far more adequate and eloquent than “daydreaming” in English.
Because Catherine discovered that part of the self-referential network is activated approximately every 20 seconds, always at the same moment in the gastric cycle between two waves of gastric contractions, which occur all the time with the same periodicity, whether we have eaten recently or not.
The implication is very interesting: 2 to 4 times per minute, the stomach invites us to a moment of self-control and reflection. Since the stomach never stops, no one completely forgets about life for too long.
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